Anybody else had as bad of luck/experience with the Ultegra 6800 cranks as me? I had the right crank arm bend and break about 3 hours into my ironman bike race 2 years ago. They replaced the crank under warranty with the same model even though a new model was available. Now almost 2 years to the day the same thing happens again!. Yes it’s been two years and I ride a 99% of the time on the trainer with a decent 350 ish FTP so there’s a fair amount of torque on the cranks but when you pay up for ultegra I expected no issues like this. Some quick research online and I find more than a few other people have had the same issue. Safe to say this will be my last set of ultegra cranks.
hasn’t happened to me but there is a BikeRadar article on the crankset Understanding a Shimano Ultegra crank failure | Exclusive - BikeRadar
Looking at my records, current bike has about 3800 miles plus an additional 90 or so hours on the trainer and no issues with the 6800 cranks.
Previous bike also had 6800 cranks and no issues after about 6700 miles.
My FTP is much lower than yours however.
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Suffice to say you’re not alone.
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Yes, I’ve gone through two and a third is starting to exhibit the “squeak” that then goes on before breakage. I’m a heavy sweater and I have a feeling that it’s due to sweat and corrosion due to high salt content in the sweat.
I recently went with a 105 R7000 crankset over Ultegra just for peace of mind.
Interestingly enough the instructions contain the following:
Check that there are no cracks in the crank arms before riding the bicycle. If there are any cracks, the
crank arm may break and you may fall off the bicycle.
Surely that’s a joke ?
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I’ve ridden ultegra 6800 for 2.5years on my main bike with no problems but that’s just one experience. Either you had bad luck or have very strong legs.
It’s not happened to me but I have absolutely seen it happen to other riders with shimano cranks.
Not at all, right on page 4:
I guess they have to cover themselves…
I also liked this, wonder if anyone has followed the instruction literally.
“The two left crank arm fixing bolts should be tightened at the same time rather than each fully tightened separately.”
I also cracked a 6800 drive side crankarm. Replaced under warranty with R8000 (and a new front derailleur). Lbs knew of this issue from the Internet but was the first time they’d seen it irl.
HUNDREDS OF PEOPLE at least. But I’m sure you’ve heard about the problem from your favorite bike equipment reviewer. What’s that? You have NOT heard about the problem from your favorite bike equipment reviewer? Hmmm. I wonder why not?
If you look at a new Ultegra crank the seams in the aluminum are a marvel of engineering. They fit together very, very well. But not well enough to be water tight. Sadly, they fit together well enough to hold water in. 
That water can be crazy stuff.
So they get a little wet. They stay a little wet & sit there long enough…pretty soon the whole crank spider cracks and falls off.
For the past three years I’ve been telling people not to use hollowtech for gravel builds. Hollowtech is a marvelous technology but it’s a paper tiger. It’s ok if your just piddling around town on a little 50 mile ride or if your riding fast in a circle with a bunch of dudes…but don’t trust it if you need a reliable solution.
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That’s generally interpreted as torquing the bolts in succession, rather than torquing one all the way then the other. Not as using two torque wrenches and 4 hands…
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They have the same warning regarding chains. That does not mean they admit all bike chains are flawed to start with.
“should be tightened at the same time” is not open to interpretation. But oddly they use the correct instruction soon after… " tightened alternately in stages"
I found it funny as you could picture 2 wrenches and 4 hands by someone following instructions to the letter
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Ditto
Hollow tech was good enough for Mark Beaumont to ride around the world on though, if I recall he did snap a crank arm and this was put down to his broken elbow causing a big pedalling imbalance.
I seem to recall reading that the large number of crank failures had happened in hot & humid areas of the world, I know of just one in my local area and that had done 15000 miles or so.
I’ve seen 2 failed shimano cranks on road bikes and one recently on a mtb.
Part of me thinks “man, that would be a scary/dangerous thing to break”
The other part of me thinks “man, I was I was strong enough to break a crank” I don’t think my cranks are in any danger.
I also question whether these aluminum crank failures might be instigated by wrecks or pedal strikes. I could see someone having a pedal strike and maybe that starts a small crack. Once a crack starts in aluminum, it’s just a matter of time before a stressed part will eventually fail.
It does make a potential case for carbon cranks over aluminum. I have carbon cranks on a couple road bikes and on both of my MTB’s. My MTB cranks have taken some big hits (not just the typical rock strikes, but catching stuff directly enough at speed to basically stop the momentum of the bike). I’m amazed how strong they are.
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Not really. The core issue is not “Aluminum vs Carbon” here. It is about manufacturing and failures as a potential result of manufacturing defect or exposure of the product in some environments.
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Carbon is not inherently free from defects. In fact, it is typical more complicated and labor intensive, which leaves the door open for it’s own set of potential failures as a result of possible defects.
This all boils down to proper design and production, regardless of the materials. Each has it’s own strength, weakness, and requirements. There is no absolute in security or risk.
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